Mesothermal Electrochemical Performance And Oxygen Reduction Kinetics Of Sr₃Fe₂O₇-based Cathode Catalysts

Ruddlesden-Popper type oxide(A_n+1B_nO_3n+1,A=rare earth and/or alkaline earth element,B=transition metal element,n=1,2,3,etc.)is a layered derivatives of the perovskite(ABO₃)material,which are developing as high-performance electrocatalysts due to their fast oxygen surface exchange kinetics and good low-and intermediate-temperature stability.In this paper,Sr₃Fe₂O_7-?oxide is used as the parent material,and the properties of the parent material are improved by doping elements in B-site and infiltrating nanoparticles to achieve better electrocatalytic effect.Sr₃Fe_2-xNi_xO_7-?and Sr₃Fe_2-xCu_xO_7-?series cathode materials were prepared by sol-gel method,and Sr₃Fe_1.9Cu_0.1O_7-?oxide was selected as the scaffold to infiltrate Pr Ox nanoparticles on the basis of the previous two chapters.From the perspective of electrocatalytic applications,its electrochemical performance as a cathode material for solid oxide fuel cells was studied.The research results show that the doping of transition metals Ni and Cu in the B-site can promote the formation of oxygen vacancies and increase the oxygen mobility in the lattice,thus effectively improving the oxygen reduction electrocatalytic activity of the cathode material;The infiltration of Pr Ox nanoparticles can extend the length of the three-phase interface,thus increasing active sites for the oxygen reduction reaction,and improving the electrocatalytic performance of the cathode material.Specifically,the doping of Ni and Cu elements can stabilize the tetragonal structure of Sr₃Fe₂O_7-?oxide.Appropriate doping of Ni³⁺and Cu²⁺ions with smaller radii leads to the unit cell volume shrinkage and increases the oxygen vacancy concentration of the material.In addition,the electrocatalytic performance and long-term stability of the cell were significantly improved after the doping modification.The Sr₃Fe_1.9Ni_0.1O_7-?cathode material has a polarization resistance of as low as 0.10?cm~2 at 700°C and has excellent chemical compatibility with GDC electrolyte materials at high temperatures,while the Sr₃Fe_1.9Cu_0.1O_7-?cathode material showing a high conductivity of 196 S cm^-1 and a peak power density of 995 m W cm^-2 at 700°C for the anode-supported full cell.The research on the mechanism of the oxygen reduction reaction found that the main rate-controlling step at the Sr₃Fe_1.9Ni_0.1O_7-?electrode was the adsorption and diffusion of oxygen molecules on the adsorption and diffusion processes on the electrode surface,while the main rate controlling step of the oxygen reduction kinetics on the Sr₃Fe_1.9Cu_0.1O_7-?electrode is the charge transfer process at the three-phase interface.Meanwhile,a single infiltration of Pr Ox nanoparticles on the Sr₃Fe_1.9Cu_0.1O_7-?oxide substrate can significantly improve the cell performance by optimizing the infiltratation process using urea decomposition,with a polarization resistance as low as 0.04?cm~2at 700°C and a peak power density of the anode-supported full cell up to 1288 m W cm^-2.These excellent electrocatalytic properties suggest that the modified Ruddlesden-Popper type oxide material is a promising cathode candidate for solid oxide fuel cells.